Interpreting postmortem drug levels
- Topic
After death, drugs move from organs into the blood, so the level measured may not be the level present in life.
What it is
Postmortem redistribution is the change in a drug's blood concentration after death. Drugs stored in organs that act as reservoirs (liver, lungs, heart, stomach) diffuse into nearby blood. That is why heart blood often shows higher values than femoral blood. The drugs most affected are basic, lipid-soluble and have a large volume of distribution. Putrefaction, breakdown of some compounds and the effects of resuscitation add to this. No single figure proves a fatal poisoning: it must be read alongside the sample, the timing, the history and the autopsy.
Key facts
- A central/peripheral ratio above one suggests redistribution, but also occurs with drugs that do not redistribute.
- The liver/peripheral blood ratio has been proposed as a more reliable marker.
- The changes depend on the time since death, body position, temperature and route of administration.
- Comparing with therapeutic and toxic ranges measured in the living has limits: the values are not equivalent.
Function
- Passive diffusion from reservoir organs (liver, lung, myocardium) into nearby blood.
- Diffusion from a stomach with gastric contents into the blood of nearby vessels and cavities.
- Autolysis and putrefaction: cells break down and release the drug; bacteria may degrade it or produce substances (for example, alcohol).
- Agonal aspiration or resuscitation: can move gastric contents or drugs and alter the central/peripheral ratio.
Next step: what to do and document
- When requesting toxicology, state where each blood sample came from; without this the figure cannot be interpreted.
- Prefer femoral blood drawn early; also keep heart blood, labelled separately.
- Record the time of death, the time of sampling and whether there was resuscitation, transfusion or drugs.
- In the report, interpret the figure with the history, the scene and the autopsy, and state its limits.
- If samples taken in life are available, send them: they are worth more than any postmortem sample.
Test yourself
Think of the answer, then tap the question to see it.
What is postmortem redistribution?
The change in a drug's blood concentration after death, mainly by diffusion from reservoir organs into nearby blood.
Which kinds of drugs redistribute most after death?
Basic, lipid-soluble drugs with a large volume of distribution, which accumulate in organs such as the lung, liver and myocardium.
Why is a high heart-blood level not enough to diagnose poisoning?
Because heart blood can rise after death through diffusion from nearby organs; it is compared with femoral blood and with the context.
Connections
Educational content on forensic and legal medicine; not legal advice and no substitute for the technical guides of Colombia's National Institute of Legal Medicine and Forensic Sciences. Laws change: each page links the official text and says when it was last checked. For a real case, follow the guide in force and ask the competent authority.
Sources: Postmortem redistribution of drugs: a literature review (Forensic Science, Medicine and Pathology, 2024); Complete republication: National Association of Medical Examiners position paper: Recommendations for the investigation, diagnosis, and certification of deaths related to opioid drugs (Journal of Medical Toxicology, 2014).
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